Conventionally, there has been known a digital multifunction printer which has a scanner function for reading a document so as to generate image data of the document and a print function for printing an image corresponding to the image data on a recording material, and which is capable of storing image data scanned by a scanner in a portable external storage device such as a memory card and a USB flash drive.
For example, Patent Literature 1 discloses a technique in which when image data is written in a USB flash drive, a flag indicating whether storage of the image data is completed or not is stored in combination with the image data in the USB flash drive, and upon mounting of the USB flash drive, it is determined whether unsuccessfully written image data is stored or not in the USB flash drive according to the flag.